Malceski and Kelly may score better, but you might just be buying in to another problem, given some of their issues this year. You also have to question just how much better Malceski or Kelly will score anyway and whether the projected points gain will be worth the trade.
I think if you were talking Hodge or Shaw, it might be a different matter, given that they might be expected to score at a significantly higher rate.
Unfortunately I've got both Smith and Lumumba on my field. If they both get 70+ each week, I'm considering it a win! I've got two trades and $50k left - part of me would love to bring in another defender (McDonald, for instance) and then loophole Smith and Lumumba for D6 each week. But I think I'm just best keeping the trades and using them in the case of injury elsewhere, because it may end up saving me more points than trying the upgrade.
At this stage of the year, I think there'd only be a few players who you'd think you could justify burning trades on to upgrade failed mid-pricers or fallen premiums. I'd have the following players on the list:
* Hodge in defence (some might make a case for Picken as well and I am certain that most already have Shaw)
* Ablett and possibly Rockliff given that he is still cheap (and assuming everyone has Fyfe, Dangerfield and Pendlebury)
* Possibly Goldstein if you are in the minority who don't have him (he is risky at his huge price though, given that most teams don't have ruck coverage)
* Deledio up forward, as he just seems to be ready to round out the year as the best scorer alongside Gray (who most people already have)
There are probably other unique options who might go alright, such as Hannebery, Zorko, Priddis and Mundy and guys like Rance and McDonald might be tempting (but with significant risk), but the benefits may not be as considerable as say adding Ablett, Hodge or Deledio to your ranks and picking up 50+ points from each compared to an under-performer.